1. Field of the Invention
This invention relates to a silicone rubber composition which quickly cures into a silicone rubber elastomer having excellent rubbery properties.
2. Prior Art
Prior art room temperature vulcanizable (RTV) silicone rubber compositions of the condensation type are generally based on a diorganopolysiloxane end-blocked with a hydrolyzable silyl group or based on a diorganopolysiloxane blocked with a hydroxysilyl group at either end and a silane or siloxane having at least three hydrolyzable silyl groups in a molecule. They are cured with the aid of curing catalysts such as tetravalent organic tin compounds and organic titanium compounds.
Among these, the former silicone rubber compositions based on a diorganopolysiloxane end-blocked with a hydrolyzable silyl group do not cure without water or humidity and are not expectable to promote curing by heating. It was difficult to cure these compositions within a short time. The latter silicone rubber compositions based on a diorganopolysiloxane blocked with a hydroxysilyl group at either end and a silane or siloxane having at least three hydrolyzable silyl groups in a molecule cure fast and are less affected by water as compared with the former compositions. However, water supply is indispensable in order to allow heavy-gage moldings of these compositions to cure to the deep inside. To this end, water, alcohol or the like is added to the compositions. Even when such a technique is employed, large sized moldings require an undesirably long time until curing is completed.
One known heat curing type of liquid silicone rubber composition is a composition of the addition curing type relying on hydroxysilylation reaction. The liquid silicone rubber compositions of heat curing type are advantageous in that the curing rate is increased by heating and the pot life is readily adjustable, but have a disadvantage associated with the use of platinum series compounds as the catalyst. When contacted with compounds having an ability to coordinate with a platinum series metal, for example, compounds or materials containing sulfur, amine or tin, the compositions are inhibited from curing due to catalyst poisoning. Therefore, the compositions are applicable only under limited conditions.